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Why the Moon Is a Copy of Earth? The Fluidity Clue ⚡ экспресс

Original: "Giant impact between high-viscosity Theia and low-viscosity proto-Earth: Origin of lunar isotopic crisis"
· Wenshuai Liu
arXiv:2606.20398 · 2026-06-18 · CC BY · ⏱ 1 min · Exoplanets
The collision of solid Theia with a liquid Earth explains why the Moon is so similar to our planet.
Abstract

Numerical modeling indicates that over 40% of the material in the circumterrestrial disk produced by the impact originates from the impactor Theia, contradicting the Earth-like isotopic composition of the Moon (isotopic crisis). Accounting for viscosity differences between the colliding bodies provides a solution: smaller planets with magma oceans cool faster and become highly viscous, while larger ones remain low-viscosity. Simulating a collision between a high-viscosity (nearly solid) Theia and a low-viscosity (molten) proto-Earth yields a disk dominated by proto-Earth material, without violating modern constraints on the angular momentum of the Earth-Moon system. This mechanism naturally explains the observed geochemical similarity.

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Young Earth was a boiling sphere of liquid rock, while Theia, which crashed into it, had had time to cool and solidify.

It’s like dropping a chunk of cold butter into a pot of soup: the soup splashes out, but the butter barely moves.

Similarly, Earth’s interior spewed into space, forming a cloud of cosmic dust and debris. From this, the Moon gradually coalesced. This hypothesis complements the standard model of the giant impact.

Analysis of lunar soil using light analysis (pioneered by Joseph von Fraunhofer) revealed that the atomic composition of the Moon and Earth is nearly identical. Decades of mystery were solved: due to the difference in fluidity, it was mostly Earth material that escaped into space. The most unexpected outcome: the Moon rocks brought back by the Apollo missions are frozen splashes of our planet. Holding them, you’re touching a shard of ancient Earth.

🎯 That same impact likely tilted Earth’s axis, giving us the seasons. So we have spring and autumn to thank that ancient catastrophe for.

Scientists
Christian DopplerD. B. McLaughlinDidier QuelozMichel MayorR. A. RossiterEmmy Noether
Tags
cosmic dust spectroscopy Standard Model
Laws
Doppler effectNoether's theoremMaxwell's equationsPlanck's lawPlanck–Einstein relationWien's displacement law
Original: arXiv:2606.20398 · CC BY · bridge42worlds